Transmit and receive diplexer for circular polarization

Abstract

A diplexer for processing polarized energy at separate transmit and receive frequencies. The nature of the polarization may be circular, linear or elliptical depending upon the phasing associated therewith. The diplexer comprises a waveguide having first and second ports disposed at opposite ends thereof. A symmetrical bandpass resonator arrangement is disposed around the periphery of the waveguide and couples energy at the receive frequency out of the waveguide. A symmetrical bandstop resonator arrangement is also disposed around the periphery of the waveguide and filters energy at the receive frequency to prevent coupling of received energy to the second port. The bandpass resonators of each of the resonator arrangements generally include tuning members that control the amount of energy coupled from the waveguide and that adjust and balance the polarization components of the energy to maintain the polarization state thereof. A plurality of tuning rings may be diposed adjacent to the first port that compensate for the impedance mismatch caused by external components coupled to the waveguide. A tuning ring may also be provided at the second port that compensates for impedance mismatch caused by the resonator arrangements. The diplexer is generally an overmoded structure that permits the propagation of higher order modes in the received energy. The symmetry provided in the bandpass resonator arrangement inhibits or prevents the excitation of these higher order modes and hence received energy not coupled out of the diplexer through the second port. Similarly, the symmetrical nature of the bandstop resonator arrangement also inhibits scattering of higher order modes and hence improves the performance of the diplexer.

What is claimed is: 
     
       1. A diplexer for processing circularly polarized energy at separate transmit and receive frequencies, the diplexer comprising: a waveguide having first and second ports disposed at opposite ends thereof;   a plurality of bandpass resonator arrangements disposed symmetrically about the periphery of said waveguide, each of said bandpass resonator arrangements including:   a first bandpass resonator protruding a predetermined length into said waveguide;   a second bandpass resonator disposed outside of said waveguide;   means for capacitively coupling said first bandpass resonator and said second bandpass resonator; and,   tuning means for tuning the resonant frequency of said first and second bandpass resonators to said receive frequency;   a plurality of coaxial transmission lines corresponding to said plurality of bandpass resonator arrangements;   means operatively associated with each one of said plurality of bandpass resonator arrangements for capacitively coupling said second bandpass resonator of each said bandpass resonator arrangement to its said corresponding coaxial transmission line;   a plurality of first bandstop resonator disposed symmetrically about the periphery of said waveguide between said second port of said waveguide and said plurality of bandpass resonator arrangements, each of said first bandstop resonators protruding a predetermined length into said waveguide and adapted to reject energy at said receive frequency to prevent transmission thereof through said second port of said waveguide; and,   wherein said tuning means and said capacitively coupling means cooperatively function to control the amount of energy at said receive frequency coupled out of said waveguide by said pluarlity of bandpass resonator arrangements, and to balance the polarization of said receive frequency energy coupled out of said waveguide by respective ones of said plurality of bandpass resonator arrangements to thereby maintain the polarization state thereof.   
     
     
       2. The diplexer as set forth in claim 1, wherein said tuning means of each one of said plurality of bandpass resonator arrangements includes: a first tuning member for adjusting the capacitance of said first bandpass resonator; and,   a second tuning member for adjusting the inductance of said second bandpass resonator.   
     
     
       3. The diplexer as set forth in claim 2, wherein said first tuning member of each one of said plurality of bandpass resonator arrangements comprises a dielectric rod which functions to add a small capacity to an end of said first bandpass resonator. 
     
     
       4. The diplexer as set forth in claim 3, wherein said second tuning member of each one of said plurality of bandpass resonator arrangements comprises a metal rod which functions to lower the inductance of said second bandpass resonator. 
     
     
       5. The diplexer as set forth in claim 1, wherein said first bandpass resonators of said plurality of bandpass resonator arrangements are evenly spaced at 90 degree intervals around the periphery of said waveguide in a common plane which is disposed perpendicular to the longitudinal axis of said waveguide. 
     
     
       6. The diplexer as set forth in claim 1, wherein said first and second bandpass resonators of each one of said plurality of bandpass resonator arrangements are TEM-type resonators. 
     
     
       7. The diplexer as set forth in claim 1, further comprising a plurality of second bandstop resonators disposed symmetrically about the periphery of said waveguide between said plurality of first bandstop resonators and said plurality of bandpass resonator arrangements, each of said second bandstop resonators protruding a predetermined length into said waveguide and adapted to reject energy at said receive frequency to prevent transmission thereof through said second port of said waveguide. 
     
     
       8. The diplexer as set forth in claim 7, further comprising tuning ring means disposed adjacent to said first port of said waveguide for compensating for impedance mismatch caused by external components coupled to said waveguide.